13
- How it works
- Interpretation of spectra
Due:

Determine the structure of this unknown (MF is C
8
H
9
Cl)

13 C NMR Correlation Chart
NH
1 H NMR Correlation Chart OH
X-C H
CO
2
H
C H O
12.0
11.0
10.0
9.0
Ar H
C=C H
O-C H
COC H
C H
3
C C H
C H , C H
2
8.0
7.0
6.0
5.0
Chemical Shift,

(ppm)
4.0
3.0
2.0
1.0
0.0

• Distinguishes between CH, CH
2
, and CH
3 carbons

13
13
13

Magnetic Resonance Imaging:
• MRI Scanner: large magnet; coils to excite nuclei, modify magnetic field, and receive
Signals
• Different tissues yield different signals
• Signals are separated into components by
Fourier transform analysis
• Each component is a specific site of origin in the patient
 a cross-sectional image of the patient’s body
QuickTime™ and a
TIFF (LZW) decompressor are needed to see this picture.
MRI showing a vertical
Cross section through a
Human head. http://en.wikipedia.org/wiki/Magnetic_resonance_imaging
How it works:
• Most signals originate from hydrogens of
Water molecules
• Water is bound to different organs in different way  variation of signal among organs & variation between healthy and diseased tissue

Some Magnetic Resonance Imaging Uses:
• Detailed images of blood vessels
• Examine the vascular tree
• Differentiate intracelluar and extracelluar edema
 stroke patients
• Detecting cancer, inflammation, tumors
Current research:
• 31 P nuclei analysis: investigate celluar metabolism (ATP and ADP)
QuickTime™ and a
TIFF (LZW) decompressor are needed to see this picture.
MRI showing a vertical
Cross section through a
Human head. http://en.wikipedia.org/wiki/Magnetic_resonance_imaging

1 H NMR:
Determine bond connectivities/pieces of a structure, whole structure
13C NMR:
Types of carbons (DEPT)
IR:
Determine the functional groups present in a structure:
-OH, C=O, C-O, NH
2
, C=C, C

C, C=N, C

N

Main Use: To detect the presence or absence of a functional group (specific bonds) in a molecule
How It Works:
1.
Bonds vibrate freely at specific wavelengths (wavenumbers)
2.
Want to cause the bonds to increase the magnitude of this vibrational frequency
3.
Subject compound to IR radiation, 4000-625 cm -1 cm -1 is the unit for wavenumber ( n
) n is directly proportional to energy (unlike wavelength)
4. Bonds absorb energy equal to their natural vibrational energy - it is quantized. This absorption of energy causes a change in dipole moment for the bond.
5. Upon absorption, bonds stretch and/or bend; the IR measures this absorption.

Stretches are more noted than bends

Specific bonds absorb specific IR radiation and signals will appear within certain wavenumber ranges (similar to NMR).
Note: O-H stretches are broader than N-H stretches
N-H Stretches:
1 ° Amines (RNH
2
) has two peaks
2 ° Amines (RNHR) has one peak
3 ° Amines (NR
3
) has no peaks

Specific bonds absorb specific IR radiation and signals will appear within certain wavenumber ranges (similar to NMR).
Correlation of Bond St retching and IR A bsorption (See also Correlation Ch art & Table in Lab
Gu ide)
Type of Bond Group
Family of Compounds Wave number Range (cm -1 )
Single Bonds —C— H Alkanes 2850-3300
Alkenes, aromatics 3000-3100 =C— H
 C—H Alkynes 3300-3320
O—H
Alcohols 3200-3600
N—H
Amines 3300-3500
C—O Ethers, E sters, Alcohols
Carboxylic Acids
1330-1000
Double Bonds C=C
Alkenes, aromatics 1600-1680
C=O
Carbonyls 1680-1750
Aldehydes, ketones 1710-1750
Carboxylic acids 1700-1725
Esters, amides
Imines
1680-1750
1500-1650
Triple Bonds
C=N
C

C
C

N
Alkynes
Nitriles
2100-2200
2200-2300

A: O-H stretch (strong, broad)
C: C-H stretch (strong, sharp)
E: C

C or C

N stretch (sharp)
F: C=O stretch (strong, medium to sharp)
G: C=C stretch (sharp)
J: C-O stretch (strong, medium)
K: C-X stretch (sharp)

IR spectrum of hexanoic acid
Functional Group Region:
1550-4000 cm -1
Most useful portion
Fingerprint Region:
400-1550 cm -1
More difficult to interpret

O-H stretches are broad due to H-bonding.

Indicate how the following pairs of compounds could be distinguished using characteristic IR peaks:
(a) Benzaldehyde (C
6
H
5
O) and benzoic acid (C
6
H
5
COOH)
1. Consider each structure:
O
H
O
OH benzaldehyde Benzoic acid
2. Determine the main differences that would be seen in IR. Use correlation chart.

An unknown oxygen-containing compound is suspected of being an alcohol, a ketone, or a carboxylic acid. Its IR spectrum shows a broad strong peak at 3100-3400 cm -1 and a strong, sharp peak at 1700 cm -1 . What kind of compound is it?
Consider what type of bonds appear in the ranges given. Refer to correlation chart.
Broad peak at 3100-3400 cm -1
Strong, sharp peak at 1700 cm

-1
